Planographic printing plate with nucleating agent and zirconium salt

ABSTRACT

A planographic printing plate having a water receptive, hydrophilic, lithographic surface, said surface having a combination of silver halide nucleating agents and a salt of zirconium, thorium or titanium.

United States Patent Stasel Keith Hoover l-lampstead, London;

James Thomas Crawford Knowles, Buckinghamshire; Wong Kwong Fa Wong YanMan, London, England 564,758

July 13,1966

Jan. 26, 1971 A. B. Dick Company Niles, III.

a corporation of Illinois July 20, 1965 Great Britain Inventors Appl.No. Filed Patented Assignee Priority PLANOGRAPHIC PRINTING PLATE WITHNUCLEATING AGENT AND ZIRCONIUM SALT 8 Claims, No Drawings US. Cl101/459, 101/462; 96/29, 96/76, 96/33 Int. Cl 841m 1/04,

[50] Field olSearch 96/29, 76; 101/1492, 456, 466, 453, 459, 462

[56] References Cited UNITED STATES PATENTS 3,220,837 11/1965 Land et a196/29 FOREIGN PATENTS 565,696 7/1960 Belgium 96/19 OTHER REFERENCESMashev, THE TECHNOLOGY OF COATED AND PROCESSED PAPER 1 PrimaryExaminerGeorge P. Lesmes Assistant ExaminerJ. P. BrammerAttorney-McDougall, Hersh, Scott & Ladd ABSTRACT: A planographicprinting plate having a water receptive, hydrophilic, lithographicsurface, said surface having a combination of silver halide nucleatingagents and a salt of zirconium, thorium or titanium.

PLANOGRAPI-IIC PRINTING PLATE WITH NUCLEATING AGENT AND ZIRCONIUM SALTThis invention is concerned with improvements in or relating toplanographic printing. In particular the invention is concerned with theprovision and use of a planographic printing plate.

In planographic printing one employs a printing plate having anoleophilic image superimposed on a hydrophilic background so that onapplication of a greasy ink to the plate wetted with water the inkpreferentially coats the image and the coated image may be used toproduce copies by an offset procedure. It is possible to manufactureplanographic printing plates having metal bases, the resultant platesbeing capable of producing tens of thousands of copies, or alternativelywhere at most only a few hundred copies are required it is more economicto employ the cheaper paper based plates. Plates of other materials,e.g., polyesters have also been proposed.

Before the plates are used to produce copies it is necessary to imagethem and often the image will be applied thereto by a typewriter or asuitable pen or pencil. However if a specimen of the image is already inexistence it would add to the expense of producing copies of this if theimage had to be recreated on the plate and it is desirable to be able totransfer the image to a planographic printing plate by physical orchemical means.

A chemical process which was not originally developed for the imaging ofmasters, but which is extensively used for the production of singlecopies, is the silver halide diffusion transfer process. This processcomprises contacting a positive paper with an exposed negative having alatent image in the presence of a developing and a fixing solutioncontaining a silver halide solvent, whereby the latent image on thenegative transfers to the positive and is developed and fixed thereon bythe solution.

There have been several proposals to adapt this diffusion transferprocess for use in conjunction with offset lithography by substituting,for the positive sheet, a specially coated or prepared sheet which islithographic or adapted to be made lithographic so that copies can beprinted therefrom on a conventional offset lithographic printingmachine. For example, aluminum plates, the surface of which has beenrendered lithographic by graining or formation of a thin layer of analuminum compound, have already been proposed for this purpose.

A process has also been proposed in which a paper base planographicprinting plate is imaged by a diffusion transfer process in which aspecial negative paper is exposed to the original and the exposednegative is processed or developed with a special developer solution.The emulsion on the negative paper consists of gelatin, silver halidesuch as silver bromide and other materials. The light exposed, developedportions of the negative are partially insolubilized and incapable oftransferring while the unexposed portions corresponding to the image tobe reproduced will transfer on contact from the negative to the papermaster surface. This is not a true diffusion transfer process becausethe colored reduced silver is formed in the gelatin layer, transferringto the master along with the gelatin film.

It is an object of the present invention to provide a planographicprinting plate which can be imaged by the silver salt diffusion transferprocess and used to produce copies simply and cheaply.

According to the present invention, therefore, there is provided amethod of producing a planographic printing plate which comprisesapplying to a base sheet having a water-insoluble, water-receptive,hydrophilic, lithographic surface, an aqueous solution of a silverhalide nucleating agent and a metal salt, said metal salt being a saltof thorium, titanium or zirconium, said solution, if desired alsocontaining a stabilizing amount of a water-soluble compatiblestabilizing agent to inhibit degradation of the nucleating agent and thesalt, whereby said surface is rendered imageable -by the silver halidediffusion transfer process. The base sheet may be of any material usedin the production of planographic printing plates, e.g., paper orcommercially available metal plates. Where the base sheet is a paperbase, the paper preferably has a dry Dennison Wax pick of at least sixand preferably over eight.

After the plate has dried it is ready for imaging, either for example bya typewriter, pen or pencil, or alternatively in a conventional silversalt diffusion transfer photocopying procedure from an existing image.The process can be used for the reproduction of line or dot-typematerial and can also be used together with half tone and continuoustone screens in the preparation of the transfer negative. Thus in orderto image the plate by the diffusion transfer technique, a diffusiontransfer negative is provided with a negative latent image, by exposureof an original in a photocopy machine, and the exposed negative ispassed through the developing section of the machine, containing anoffset developer, in contact with the planographic printing plateaccording to the invention so that the latent negative image on thetransfer negative diffuses, on development, to the surface of theprinting plate of the invention which has been treated with the aqueoussolution of nucleating agent and metal salt. After separating the twosheets, the image is fixed, simply by applying a fixing solution and theprinting plate is then ready for use on a conventional offset printingmachine after fixing the image.

Coated papers having a lithographic surface, a good wet strength and adry Dennison Wax pick of eight or higher and preferably above,l1 mayconveniently be used as the base sheet. For most purposes we recommendthat the pick resistance be over eight.- A high pick resistancefacilitates separation of the master from the exposed negative and alsoresults in a cleaner background on the copies printed.

In order to render the surface of paper base sheets lithographic it isnecessary to coat the surface with an organic binder and a filler.Various binders such as casein, starch, carboxymethyl cellulose,polyacrylic acid, polyvinyl acetate, alginic acid, polyvinyl pyrrolidoneand polyvinyl chloride may be used providing they form a lithographicsurface when mixed with a hydrophilic filler. However, casein has beenfound to provide the best results. The binder may be used as such but ispreferably used together with a pigment.

Planographic printing plates according to the invention may bemanufactured from the papers termed in the trade as Art Papers, i.e.,papers already coated with a binder and filler, provided the surface ofthe paper has a dry Dennison Wax pick of at least six and islithographic.

The planographic printing plates may also be prepared from direct image[paper base planographic printing plates provided these have been coatedand filled as described. These plates may then be coated with an aqueoussolution of nucleating agent and metal salt as described. These paperbase plates, which were primarily intended for use as direct imagemasters for imaging, e.g., using a typewriter, generally consist of ahigh wet strength paper coated with a pigment, e.g., clay or zinc oxideand a binder, e.g., casein. The surface of these masters is alreadylithographic, having been so rendered by any of the conventional methodssuch as by brushing or treatment with a salt, e.g., zinc chloride.

The planographic printing plates according to the invention may bemanufactured by conventional techniques and the metal salt andnucleating agent may be applied at a suitable point during manufacture,i.e., not necessarily after the plate is otherwise finished. Where aproper base is employed the metal salt and nucleating agent may thus beapplied before or after a calendering step and before or after theapplication of a wash coat.

The aqueous composition used in the present invention also preferablycontains a stabilizing agent, as stated, in order to preventdeterioration of the composition on the base sheet. lf the base sheet isto bestored for any length of time then the presence of the stabilizingagent may be essential in order to achieve good printing results. Thus,in the absence of the stabilizer under such conditions, a waterimpermeable coating is formed on the base sheet and this reduces thehydrophilic properties of the latter which are necessary to the successof planographic printing.

Any convenient stabilizing agent may be used always provided it issufficiently soluble in water and does not oxidize silver. Examples ofsuitable stabilizing agents (as evidenced by accelerated ageing tests)include strong nonoxidizing acids such as dilute mineral acids, e.g.,dilute hydrochloric acid or dilute nitric acid and also compatiblesoluble phenols such as phenol itself, quinol, pyrogallol,phluoroglucinol or resorcinol. As is known, polyhydric phenols withorthoor para-hydroxy groups and their ethers are antioxidants. Examplesof such antioxidants include gallic acid and lower alkyl esters thereof,catechol, various ethers of quinol (e.g., lower alkyl and benzyl ethers)and quinone. Various phenols are unsatisfactory owing to incompatibilitywith the composition, e.g., due to their forming insoluble precipitateswith the nucleating agent or the metal salt or by being per se notsufficiently soluble soluble.

Nucleating agents for silver halides in diffusion transfer processes areknown for example from US. Pat. No. 2,352,014 and British Pat. No.614,155 and are able to reduce silver halides in the absence of light.They are also known as fogging agents. The preferred nucleating agentsare the stannous halides, e.g., stannous chloride, fluoride or bromideparticularly stannous chloride.

The nucleating agent and metal sat salt may be coated onto the basesheet from two separate solutions, one of which may conveniently containthe stabilizers, antioxidants or pigments etc.

Since suitable lithographic paper base sheets are already commerciallyavailable and further since the nucleating agent and metal salt areprone to degradation as stated, it may be preferable to treat thesurface of e.g., a direct image master or an Art Paper with the aqueoussolution just prior to imaging by the diffusion transfer process.

It is thus also an object of the present invention to provide a solutionsuitable for converting a base sheet having suitable characteristics asstated, to a planographic printing plate which can be imaged by thesilver salt diffusion transfer process.

According to the present invention therefore there is provided anaqueous solution comprising a silver halide fogging or nucleating agentand a salt of thorium, titanium or zirconium (the metal salt). Thefogging agent and the metal salt can also be applied to the base sheetin separate solutions and if the master is not to be used reasonablysoon thereafter the water compatible stabilizer may be incorporated intoone or other of the solutions preferably into the metal salt solution.In any case a short period should be allowed in between applying thesolutions, and also before the master is used, to allow it to dry off.

The air dry weight of the coating of nucleating agent, metal salt, andstabilizer when present, is variable over a wide range, e.g., from 0.6to 16 grams per square metre. A preferred range for the weight of thecoating is 0.6 to 14 g.s.m. The optimum coating weight will depend onthe nature of various factors including the ability of the substrate toabsorb the aqueous solution. In general absorbent base sheets, e.g.,absorbent papers, will require more solution to be used than relativelynonabsorbent base sheets. However preliminary trial and error experimentwill soon indicate the optimum coating weight. For less absorbent basesheets coating weights of from 0.6 to 3 g.s.m. are convenient and formore absorbent base sheets, especially certain papers, not less than2.45 g.s.m., e.g., 5 to 9 preferably 6 to 8 g.s.m. may be used.

The amount of stabilizer used will depend on the required shelf life ofthe master but will generally be at least 10 percent and not more than60 percent by weight of the coating. Satisfactory results can beobtained in most instances by using about 50 percent.

The ratio by weight of nucleating agent to metal salt in the coating maybe with the range of from l.0:O.87 to l.O:l0.4, e.g., from 1.0:l.0 or1.0:] .3 up to l.0:2.0 or 1.020.87 to 1.8:;064, l.O:5.2 and aparticularly preferred ratio being about I.

Apart from the ratio limitations too little nucleating agent or metalsalt will result in a brown nonink receptive image whilst too muchnucleating agent will initially produce a dense bronzy image on themaster but an image which is easily washed off during the fixing andetching processes. This has been attributed to the film formingproperties of the metal salt used.

The actual amount of nucleating agent, metal salt and optionallystabilizer in the aqueous cooling solution or solutions is thus adaptedto provide an air dried coating having the characteristics set forthabove. The solution must not be of such a concentration that thecompounds in the solution are liable to precipitate at room temperature.Conversely if the dilution is too great an excessive amount of thesolution will have to be applied.

The preferred concentration of the compounds in the aqueous solutiondepends on the desired coating weight and the solubility of theconstituents but may conveniently be from 2.6 percent to 17 percent byweight. Particularly preferred weight percentages for the concentrationof the coating solution are from 5.25 percent to 9.6 percent andespecially from 6.25 percent to 8.6 percent by weight. In the solutionthe ratio by weight of nucleating agent to metal salts and the amount ofstabilizer will be as for the respective amounts in the coating to belaid down on the base sheet.

The metal salt used may be an acetate, chloride or nitrate, e.g.,zirconyl acetate, zirconyl nitrate, thorium nitrate, thorium chloride,titanium dichloride or zirconyl chloride. The metal salt used must notbe one which destroys the lithographic properties of the surface of themaster.

The diffusion transfer negative used is of the conventional type and maybe one of those commercially available and intended for use in theproduction of single copies by the diffusion transfer method. Inparticular the following can be used: Gevart GS (Gevart Photo ProductionAntwerp, Belgium) Oricopy (Oriental Photocopy Company, Tokyo, Japan) andAnken Photo Rapid negative made by Anken Chemical Company, New Jersey,USA.

The developer used may be any of the conventional offsettype developers.These are reducing solutions which contain a solvent for the silverhalide, a synthetic gum, an antioxidant and other stabilizers. A typicalexample is the offset developer made for the Diffusion Transfer Processby Gevart and also A. B. Dicks developer formula 59B9.2. 9.2.

The fixing solution is again conventional and may for example be CTOffset Fixer made by Kodak (Trade Mark). This fixer appears to containinter alia carboxy methyl cellulose, sodium nitrate, sodium thiosulfate,ammonium phosphate, ethyl alcohol a small amount of a mercapto compoundand water. Solutions of this type are described in British Pat. No.934,691.

The invention will now be illustrated with reference to the followingTables of experimental results.

EXPERIMENTAL Table I illustrates the invention with respect to varioustypes of paper which may be used.

In examples 1 to 6 inclusive and 8 the base sheets used were commercialwet strength papers coated with a pigment and a binder as specified. Thesurface of the paper was then made lithographic by conventional means,e.g., by brushing or washing with a salt such as zinc chloride.

In examples 7and 9 art type papers were used. In all cases the followingsolution was used:

Stannous Chloride 1 gram.

Zirconyl Acetate 20 of 13 percent solution in water. Phenol 4 grams.

Water ml.

The solution was applied by conventional coating means such that the airdried coating weight was 6 to 8 grams per square metre. The coated anddried sheet was then calendered until the surface was smooth and thesheet flat. The paper master, so made, was contacted with a properlyexposed Gevart type GS negative sheet and passed through Gevart OffsetDeveloper solution of the instructed dilution in an A. B. Dick M. 120Photocopier. After about 14 seconds the two sheets were separated. Theimage on the master was fixed by applying a Kodak (Trade Mark) CT Offsetdeveloper solution using a cotton pad. The imaged master was then usedto produce copies on a conventional offset duplicator.

The wet strength papers coated as above can give up to 2,000 goodcopies.

TABLE I Resist- Ex. ance No. Pick Type of coating Comments 1. 12Casein-Pigment Very good copy, long run. 2..... 11 .....do Good copy,short run. 3. 14 Starch-Pigment Do. 4..... 8 Polyacrylic acid-pigmentFair to poor copy. 5. 12 Polyvinyl copolymers-pigment Fair to poor. 6...11 Carboxymethyl cellulose-pigment... Fair copy. 7... 6 Casein Fair topoor copy. very short run. 8.. 12 Casein-pigment Very good co y, mediumrun. 9".-. 9 Casein-latex-pigment Good copy, s ort run.

When stannous fluoride was substituted for stannous chloride in exampleNo. 2 a master was obtained which gave incomplete transfer but the copywas otherwise fair. Likewise use of stannous bromide resulted inincomplete transfer and fair to poor copy.

Table II gives the results obtained when example 2 was repeated usingother metal salts according to the invention in place of zirconylacetate:

TABLE IL-SUBSTITUTION FOR ZIRCONYL ACETATE IN STANDARD FORMULA No.Zirconyl acetate substitute Comments 10. Zirconium nitrate Dense bronzyimage. Fair copy.

11 Thorium nitrate Ptgirttransier. Slightly bronzy image. Some copy upoor.

12.... Thorium nitrate heated one hour at 100 C Better transfer and copythan Example 11.

Thorium chloride Fair transfer. Fair copy.

Titanium chloride..... Fair bronzy image. Fair to good copy. 15 Zirconylchloride Uneven transfer. Fair to good copy. Image bronzy in some areas.16 Zirconyl chloride heated one hour at 100 0...... Fairly dense bronzyimage. Fair to good copy.

TABLE IIL-PRESERVING AGENTS Aging. hrs. at Ex. No. Preservative 100 0.Comments 17 None None Good bronzy image on Master. Good copy. Clearbackground. 18 o 1 Fair bronze image on Master. Poor copy. Speckybackground. 19 ..d 17 Faint image. No copy. 20 PhenoL. 1 Good bronzyimage and copy. Specks. 21 ..do 17 Fair bronzy image. Fair copy. 22Resorcinol 17 Bronzy image. Fair copy. Scums. 23.. Phloroglucinol.-.. 17Bronzy image in areas. Fair copy. 24.. Hydroquinone. 17 Good bronzyimage. Good copy. Some scum. 25.. None Fair bronzy image. Fair copy. 2617 Slight bronzy image. Poor copy. 27 17 Good bronzy image. Fair to goodcopy. 28 17 Weak bronzy image. Fair copy. Clean background. 29 17 Fairbronzy image. Fair copy. Clean background. 30... 17 Good bronzy imageand copy. Clean background.

From a commercial standpoint masters made as above described would beexpected to have a shelf life of at least 1 year if stored under normalconditions. In order to short cut Table IV shows the effect usingvarying quantities of stabil izer according to the present invention.Examples 31-33 usethe paper and solution of example 25 and examples34-36 the length of time required to evaluate preservatives. an acusethe paper and solution of example 22. In both cases the 4 percent ofphenol used in the solution of earlier examples was replaced by theamounts of phenol shown in table 1V.

8. We claim: 1. A planographic printing plate having a water insoluble,

The effect of changing the air dried weight of the coating is shown inthe following table V. In examples 37-39 the solution and paper ofexample 8 was used.

TAB LE V Air dry coating weight,

g.s.m. Comments Fair bronzy image. Fair to poor copy. Good bronzy image.Fair copy. Fair bronzy image. Fair to poor copy.

TABLE VI water receptive, hydrophilic, lithographic surface, said platehaving on the lithographic surface the combination of a nucleating agentfor silver halide and a water soluble salt of zirconium as a componentseparate and apart from the nucleating agent to render said surfaceimageable by the silver halide diffusion transfer process, the materialsbeing present in the ratio of one part by weight nucleating agent to0.87 to 10.4 parts by weight of the zirconium salt.

2. A plate as claimed in claim 1 in which the combination on thelithographic surface contains 10-60 percent by weight of a water solublecompatible stabilizing agent to inhibit degradation of said nucleatingagent and said salt.

3. A plate as claimed in claim 2 in which the stabilizing agent is acompatible water-soluble phenolic compound.

4. A plate as claimed in claim 1 having a paper base, said base having acoating of an organic binder and a filler on the surface thereof andhaving a dry Dennison wax pick of at least SIX.

5. A plate as claimed in claim 1 wherein said lithographic surface is inthe form of a coating containing a binder of casein.

6. A plate as claimed in claim 1 wherein said metal salt is zirconylacetate, zirconyl nitrate or zirconyl chloride.

Percent in solution image washes off. Very slight poor copy.

Although the above examples illustrate the application of 7. A plate asclaimed in claim 1 wherein the nucleating the invention with paper basemasters, it is to be understood agent isastannous halide.

that the invention is not limited thereto and that other lithographicmasters having, for example, metal or plastic substrates may be used. Anexample of a plastic base master is the 8. A plate as claimed in claim 1wherein the nucleating agent and zirconium salt are present in separatecoatings on the surface of the plate.

polyester based Transmaster D1 of the Ozalid Company.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,557696 Dated January 26 1971 Inventor) Stasel Keith Hoover et a1 It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3 lines 73 and 74 cancel "1 0:0 .87 to 1 .0:10 .4" Column 4 line5 after "attributed" insert in some cases line 45 after "59B9. 2" cancel"9 2"; line 68 after "20" insert m1 Column 5 line 2 "14" should read 1SSigned and sealed this 15th day of June 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, J Attesting OfficerCommissioner of Patent

2. A plate as claimed in claim 1 in which the combination on thelithographic surface contains 10-60 percent by weight of a water solublecompatible stabilizing agent to inhibit degradation of said nucleatingagent and said salt.
 3. A plate as claimed in claim 2 in which thestabilizing agent is a compatible water-soluble phenolic compound.
 4. Aplate as claimed in claim 1 having a paper base, said base having acoating of an organic binder and a filler on the surface thereof andhaving a dry Dennison wax pick of at least six.
 5. A plate as claimed inclaim 1 wherein said lithographic surface is in the form of a coatingcontaining a binder of casein.
 6. A plate as claimed in claim 1 whereinsaid metal salt is zirconyl acetate, zirconyl nitrate or zirconylchloride.
 7. A plate as claimed in claim 1 wherein the nucleating agentis a stannous halide.
 8. A plate as claimed in claim 1 wherein thenucleating agent and zirconium salt are present in separate coatings onthe surface of the plate.